1. Field of the Invention
This invention relates to an improved process for producing a mixture of branched and linear carboxylic acid salts, in particular, an improved process which produces a reaction mixture having a reduced tendency to foam and solidify, thus permitting the reaction to proceed to completion and permitting the easy removal of the reaction mixture from the reaction zone. The process, additionally, insures that the branched and linear mixture of carboxylic acid salts produced substantially corresponds to the branched and linear mixture of alcohols reacted.
2. Prior Art
Carboxylic acid salts and acids derived therefrom are useful for the preparation of high quality bar soaps and other soap products, the preparation of various types of esters for various purposes such as lubricants, hydraulic fluids, edible oils and fats and numerous applications as intermediates in the preparation of a wide variety of chemical compounds. Mixtures of branched and linear carboxylic acids are particularly important for the production of the corresponding esters for use as lubricants or functional fluids, see U.S. Pat. Nos. 4,053,491 and 4,144,183 both to Koch et al.
The preparation of carboxylic acid salts and of carboxylic acids via the caustic fusion reaction of alcohols, with or without a catalyst, is a process that has been known for many years (see, for example, Dumas and Stas, Ann., 35, 129-173, 1840 and U.S. Pat. No. 2,384,817 to Chitwood). This process has of comparatively recent date become associated with the preparation of high purity salts and acids of a type capable of effective direct substitution for naturally derived salts and carboxylic acids in large use areas, such as manufacture of high quality soap products where cost is an important factor, and the production of esters for use in hydraulic fluids and lubricants. One possible reason for this is that it was only recently that synthetic alcohols of high purity and low cost became available in quantities sufficient for consideration as raw materials for the production of such salts and acids. Until this stage of technology was reached, the usual derivation of alcohols was from the acid components of ester materials in natural source oils and fats such as coconut oil. Thus, prior large scale processing was directed to producing alcohols from acid structures, not vice versa, and this for the most part made natural source derived alcohols more costly than natural source salts and acids; thus, there was no prior reason for considering large scale production of natural source type salts and acids from alcohols by a caustic fusion process or by any process for that matter.
The caustic fusion reaction of alcohols, i.e. reacting an alcohol (ROH) with a caustic M(OH).sub.n, to produce carboxylic salts, as indicated previously, is well known in the art, and various improvements on the process and variations thereof are described in, for example, the following U.S. Patents: U.S. Pat. No. 2,384,817 to Chitwood; U.S. Pat. No. 2,614,122 to Mikeska (which describes preparing dodecanedioic acid by cleaving 12-hydroxystearic acid with an alkali metal hydroxide in the presence of high boiling saturated petroleum hydrocarbons solvent resulting in a viscous emulsified mass which is difficult to purify); U.S. Pat. No. 2,696,501 to Stein; U.S. Pat. No. 2,847,466 to Steadmann et al (which describes a caustic fusion reaction in the presence of water); U.S. Pat. No. 3,121,728 to Bartlett; U.S. Pat. No. 3,227,737 to Ashworth; U.S. Pat. No. 3,365,476 to Dimond et al. (I); U.S. Pat. No. 3,370,074 to Dimond et al. (II); U.S. Pat. No. 3,449,413 to Hartel et al.; U.S. Pat. No. 3,503,896 to Fishman; U.S. Pat. No. 3,558,678 to Fanning (I); U.S. Pat. No. 3,560,537 to Eller; U.S. Pat. No. 3,657,293 to Fanning (II); U.S. Pat. No. 3,671,581 to Keenan; U.S. Pat. No. 3,717,676 to Bechara et al; U.S. Pat. No. 3,806,529 to Havinga et al; U.S. Pat. No. 3,864,369 Isa et al. (I); U.S. Pat. No. 3,910,973 to Isa et al. (II); and U.S. Pat. No. 3,957,838 to Nishino et al.
Generally, the known process (i.e. the caustic fusion reaction of alcohols) consists of reacting an alcohol of the formula RCH.sub.2 OH with a caustic of the formula M(OH).sub.n to produce a reaction mixture containing the carboxylic acid salts of the formula: ##STR1## wherein R is generally an alkyl substituent and M is an akali metal or an alkaline earth metal, usually sodium. The process liberates hydrogen.
The reaction may be carried out with or without a catalyst. Catalysts such as solid carbon, zinc, zinc oxide, cadmium, etc. have been used. The process may be accomplished under pressure or under atmospheric conditions and under varying temperature conditions.
Problems which have plagued this particular process are a tendency of the reaction mixture to foam, to form solid foams and to form a solidified reaction mixture. The foaming is generally caused by the agitation of the reaction mixture and the rapid liberation of hydrogen. This foaming can be extensive and cause the shutdown of the reaction. The formation of solid foams and a solid reaction mixture is probably due to the fact that the melting point of the carboxylic acid salts produced may be higher than the reaction temperature or higher than the temperature which the reaction mixture is cooled down to, for performance on the reaction mixture of a subsequent process step, e.g. acidification to carboxylic acid. Solid foam is probably formed when hydrogen, which is liberated from the reaction mixture, becomes entrapped in the solidifying reaction mixture. The solid foam and solidified reaction mixture make it extremely difficult to remove the reaction mixture from the reaction zone for conveyance to a subsequent process step or the performance of a subsequent step on the reaction mixture.
An additional problem occurs when reacting a mixture of branched and linear alcohols in that the reaction does not produce a mixture of branched and linear carboxylic acid salts which substantially corresponds to the alcohol mixture. The reaction tends to favor the production of linear carboxylic acid salts due to the greater activity of the linear alcohols.
All of the aforementioned problems are particularly prevalent in reacting alcohols of higher chain lengths, i.e. R equal to or greater than 5, but may be present when reacting lower chain length alcohols.